We fairly often get inquiries from people with good intentions who want to know about pre-tied tzitzit. This week we received an inquiry from a lady making a tallit for her grandson's bar mitzvah. 

Shalom. I have created a tallit of silk for my grandon's bar mitzvah. I am looking for kosher pre-tied tallit strings for the corners. I would prefer the ones with the blue strings in them. Do you carry this or know where I can get them? Thank you, Judy

I explained to Judy that "kosher" and "pre-tied" is a contradiction in terms. If it's pre-tied, it's not kosher.

The Torah says tzitzit must be tied on the garment. As the Talmudic Sages explain, they cannot be tied and then attached. If you come across such pre-tied strings they are not kosher by any stretch of the imagination and in all likelihood are sold and used by certain Jewish Messianic (i.e. today's Jews for J) groups that latch onto various mitzvahs.

Kosher tzitzit strings must be spun with the intent to fulfill the mitzvah (see “Kosher Tzitzit Strings: A Matter of Intent“).

You can buy kosher tzitzit strings, including techelet, here and you can find tying instructions here. In most congregations there is someone who can help bar mitzvah boys tie on tzitzit.